Air pollution is generally defined as an unacceptable concentration of one or more air contaminants. Usually air pollution indicates actual or potential adverse health effects for sensitive personnel. Air pollution control programs must, by law in the United States, respond to air pollution with emission reduction requirements. This often means shifting costs of reducing pollution to an emission source or emission sources. Data from air quality monitoring networks are very important, both to describe air pollution problems in terms of geographic extent and magnitude and to measure changes due to emission reductions or increases. High quality air monitoring data ensure that air pollution control programs adequately protect the public health and safety while keeping costs of reducing that pollution as low as possible.
Ideally, there would be full knowledge of air pollutant concentrations at all points and times within geographic areas of concern. However, from a practical standpoint, acquiring such knowledge through continuous monitoring is prohibitively expensive. Sampling and monitoring activities and equipment are expensive. In addition, power and security concerns limit the number of available sites where an agency can gather air quality data at reasonable costs.
Site selection for monitoring is therefore very important. Public confidence in the data is maintained only as long as there is an assurance that the data are representative. It is very difficult, however, to adequately provide an indication of air quality in all areas with one or only a few monitoring sites.
One method of addressing these data gaps is to model an area using selective meteorological and emissions information. This method is frequently used to estimate where and how much air pollution exists. Modeling is a useful technique that relies extensively on the accuracy of collected emissions and meteorological data. Survey sampling and saturation monitoring techniques can be used to augment or verify model values, to define problem areas and to validate monitoring sites.
To provide such sampling, it is desirable for a survey sampler to be portable and capable of relatively long operation, at least up to twenty-four hours. It is also necessary, for certain applications, for the sampler to operate at a flow rate high enough to separate particles below ten micrometers. Such separation, typically requiring flows of five liters per minute, usually involves the use of pumps having appreciable energy requirements. It is also useful to be able to monitor both for particulate material and gaseous pollutants at the same time.
To meet all of these requirements, it is generally not possible to monitor continuously over a twenty-four hour period. Instead, it is necessary to monitor at particular times of greatest interest.
However, because of varying air pollution conditions at different times of the day, it is not acceptable to mix samples taken during different times of a particular day.
Sampling devices have been reported in the prior art, but none teach the apparatus claimed, or achieve the objectives of the current invention. U.S. Pat. No. 5,074,137 issued to Harris, et al. claims a "Programmable Atmospheric Stabilizer." The device disclosed in the Harris patent does not store samples for subsequent analysis, but rather measures an air stream for a particular, pre-determined pollutant. The Harris device cannot be used for quantitative measurements. It only serves to detect whether a particular gas has exceeded a particular threshold. Finally, the Harris device is not portable, and in one embodiment the sampling device is fixed to a storage container or room that contains the material of concern.
U.S. Pat. No. 4,800,763 issued to Hakkers, et al. is directed toward a method and apparatus for drawing and analyzing samples from a fluid stream whereby successive samples of a particular analyte are collected for analysis with the results compared against previous samples. The method disclosed in the Hakkers patent does not comprehend collection of different types of samples during the same procedure. It is not directed toward independent control of the sampling parameters for each sample. The Hakkers patent also does not disclose a portable device.
U.S. Pat. No. 4,432,248 issued to Lalin discloses a portable, battery operated gas sampling device. However, the sampling device of Lalin has only a single gas collection chamber, and the particulate filter is primarily used for trapping particles that interfere with the subsequent collection and analysis of the single gaseous sample. Neither does the Lalin patent disclose independent control of sampling parameters for plural samples. The Lalin patent also teaches away from a low flow warning or shut-down, relying rather on visual means for determining that the particulate filter has become clogged.
It is, accordingly, an object of the present invention to provide a new and improved apparatus for sampling environmental air at diverse times during the day.
It is still another object of the invention to provide a new and improved apparatus for enabling samples of environmental air taken at different times of a day to be separated, for subsequent analysis.
It is also an object of this invention to collect particulate matter for analysis, and over the same time period, collect gaseous samples as well using the same device.
It is also an object of this invention to be able to be able to flexibly program the collection of the gaseous samples so that samples are collected: a) in one sample collection container over one time period and another sample collection container over another time period, or alternatively b) into the plural sample collection containers over the same time periods.
It is another object of the present invention to provide an electrically operated, portable air sampler powered by a battery and that can operate with a constant flow rate, wherein operation of the pump is prevented when the voltage of the battery driving the pump drops below a predetermined level, or when the flow rate of the drawn gas drops below a predetermined level. When the pump is thus prevented from operating, operation of the pump should not automatically resume if the battery voltage or flow rate of the drawn gas again rise above those predetermined levels.